Mole rats spend nearly all their lives underground, but they
are not blind
as was long thought, and are even color-sensitive, new research confirms.

Anatomical research has shown that the tiny eyes of these
subterranean creatures are ill-suited for their activities of navigating dark
tunnels and making rare trips aboveground.

However, mole rats also plug their tunnels to keep out
predators. According to a Czech study, two species of African mole rats
appeared to use their limited vision to do so.

Detecting light from holes in their tunnels enables mole
rats to quickly plug the holes to keep out predators like honey badgers and
humans.

"Mole rats are a traditional food in many African
regions," study researcher Ondřej Kott, a doctoral student at the
University of South Bohemia, wrote in an e-mail.

In addition to detecting light, mole rats showed a limited sensitivity
to colors during the researchers' experiments. They responded to blue and
green-yellow light, but not to red. It was unclear whether they can distinguish
between blue and green or green-yellow.

In the maze

To simulate a hole-plugging scenario, the researchers placed
the silvery mole rat and the giant mole rat into a maze of Plexiglas tunnels
containing horticultural peat. Once they had the animals inside, the
researchers covered the maze but illuminated the end of one tunnel with a 40-watt
incandescent bulb. They then recorded whether the mole rats used the peat to block
the light.

The giant mole rat tried to plug the hole in 80 percent of
trials, and the silvery mole rat did so 85 percent of the time.

In a related test, mole rats were supplied with food and
nesting material and given the choice between two nesting boxes, one dark and
the other illuminated by white or monochromatic light. After 60 and 90 minutes,
researchers checked the nesting boxes to see where the mole rats had settled
down.

Mole rats preferred the dark box, avoiding the boxes
illuminated by white, blue, or green-yellow light. However, they seemed to have
no preference between a dark box and a box illuminated by red light,
suggesting the animals couldn't detect red.

Life underground

The first behavioral evidence that mole rats can distinguish
between light and dark was reported in 2006, according to Kott. With this latest
study, the ability to discriminate between light and dark is documented in five
species of African mole rats. Separate research has characterized the eye and
neural anatomy in 11 of the 22 known species.

"Broadly speaking, all species are well-equipped for image-forming
vision but severely constrained in terms of visual acuity," Kott told
LiveScience. In this family of rodents, "the brain only resolves a
coarsely 'pixelated' image of the outside world."

There is plenty of other evidence that these subterranean
rodents have not adapted to use their eyes in dark tunnels or aboveground. Most
African mole rats have small lenses in their eyes that do not effectively
collect light, and they lack the adaptations seen in nocturnal mammals for low-light
vision.
They also appear poorly equipped to orient themselves in the three-dimensional
environment they would encounter on the ground, according to Kott.

African mole rats are not alone among subterranean mammals
in possessing limited vision. Light-avoidance behavior has been documented in
moles and in the misleadingly named blind mole rat. (Blind mole rats are not
members of the African mole rat family.)

Wynne Parry

Wynne was a reporter at The Stamford Advocate. She has interned at Discover magazine and has freelanced for The New York Times and Scientific American's web site. She has a masters in journalism from Columbia University and a bachelor's degree in biology from the University of Utah.